Method and apparatus enabling fast channel change for DSL system

ABSTRACT

There is provided methods and apparatus for enabling a fast channel change for a Digital Subscriber Line (DSL) system. A channel change processing unit for enabling a channel change in a DSL system includes a demultiplexer ( 132 ) and a selector ( 134 ) in signal communication with the demultiplexer. The demultiplexer ( 132 ) is for receiving a normal stream and a channel change stream. The selector ( 134 ) is for receiving a channel change request and for sending the channel change stream in response to receiving the channel change request. The channel change stream coded pictures are of a lower quality than the normal stream coded pictures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 60/567,483, filed May 3, 2004, which is incorporated by referenceherein in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to Digital Subscriber Line (DSL)systems and, more particularly, to a method and apparatus for enabling afast channel change for a DSL system.

BACKGROUND OF THE INVENTION

In a commercial video over DSL broadcast system, it is desirable toallow end users to be able to change channels rapidly. Popular videocompression standards, such as MPEG-2 and JVT/H.264/MPEG AVC use intraand inter coding. For proper decoding, a decoder must decode acompressed video sequence beginning with an intra-coded (I) picture, andthen continue to decode the subsequent inter-coded (P and B) pictures. AGroup of Pictures (GOP) may include an I picture and several subsequentP and B pictures. I pictures typically require many more bits to codethan does a P or B picture of equivalent video quality, in the range of3 to 10 times more bits. When a receiver initially begins receiving aprogram on a particular channel, following a channel change or initialturning on of the receiver, it must wait until an I picture is receivedto begin decoding properly, which causes a delay.

To minimize channel change delay in digital video broadcast systems, Ipictures are typically sent frequently, for example every N pictures.For example, to enable a ½ second delay (of the video compressionportion of the system), it is common to use N=15 for 30 frames persecond (fps) content. Since compressed I pictures are so much largerthan compressed P and B pictures, this considerably increases thebitrate over what would be required if I pictures were not inserted sofrequently.

In some systems, instead of sending full I pictures frequently, atechnique called “progressive refresh” is used, where sections ofpictures are intra coded. Typically, all macroblocks in the picture areintra-coded at least once during an N-picture period. In theJVT/H.264/MPEG AVC compression standard, P and B pictures may bepredicted using multiple reference pictures, including the picturesbefore a preceding I picture. The standard identifies random accesspoints as Independent Decoder Refreshes, or IDRs, which constrain thatno reference pictures before the IDR are used in predicting picturesfollowing the IDR. Pictures may be coded using slices of differenttypes. A picture in which all coded slices are of type I may be referredto as an I picture.

The JVT/H.264/MPEG AVC compression standard includes a tool calledredundant pictures, defined in the standard as follows:

-   -   redundant coded picture: A coded representation of a picture or        a part of a picture. The content of a redundant coded picture        shall not be used by the decoding process for a bitstream        conforming to this Recommendation I International Standard. A        redundant coded picture is not required to contain all        macroblocks in the primary coded picture. Redundant coded        pictures have no normative effect on the decoding process. See        also primary coded picture.

The slice header contains a redundant_pic_cnt field, whose semantics aredefined in the JVT/H.264/MPEG AVC compression standard as follows:

-   -   redundant_pic_cnt shall be equal to 0 for slices and slice data        partitions belonging to the primary coded picture. The        redundant_pic_cnt shall be greater than 0 for coded slices and        coded slice data partitions in redundant coded pictures. When        redundant_pic_cnt is not present, its value shall be inferred to        be equal to 0. The value of redundant_pic_cnt shall be in the        range of 0 to 127, inclusive.    -   If the syntax elements of a slice data partition A RBSP indicate        the presence of any syntax elements of category 3 in the slice        data for a slice, a slice data partition B RBSP shall be present        having the same value of slice_id and redundant_pic_cnt as in        the slice data partition A RBSP.    -   Otherwise (the syntax elements of a slice data partition A RBSP        do not indicate the presence of any syntax elements of category        3 in the slice data for a slice), no slice data partition B RBSP        shall be present having the same value of slice_id and        redundant_pic_cnt as in the slice data partition A RBSP.

A system has been proposed wherein a channel change stream is encodedand transmitted along with the normal video bitstream. The channelchange stream includes lower quality I pictures that are sent at ahigher frequency than I pictures in the normal bitstream. When a usertunes to a new channel, playback could begin upon receipt of the first Ipictures, in either the normal or channel change stream. This system istargeted at an end-to-end broadcast system, without any upstreamindication of a channel change or possibility for storage atintermediate points in the system. By incorporating upstream channelchange indications and/or intermediate storage points, the presentinvention can reduce bandwidth requirements over the most bandwidthcritical links of the end-to-end system and increase channel changeresponse time.

Another system has been proposed wherein a reduced resolution updatecodec is employed such that prediction residuals can be coded at lowerresolutions for some of the coded pictures in a sequence, while othercoded pictures in a sequence are coded at the full resolution. However,this system does not provide any capability for improved channel changeefficiency.

SUMMARY OF THE INVENTION

These and other drawbacks and disadvantages of the prior art areaddressed by the present invention, which is directed to a method andapparatus for enabling a fast channel change for a DSL system.Advantageously, the present invention advantageously allows for achannel change delay at any desired rate at a lower bitrate than priorart methods.

According to an aspect of the present invention, there is provided achannel change processing unit for enabling a channel change in aDigital Subscriber Line (DSL) system. The channel change processing unitincludes a demultiplexer and a selector in signal communication with thedemultiplexer. The demultiplexer is for receiving a normal stream and achannel change stream. The selector is for receiving a channel changerequest and for sending the channel change stream in response toreceiving the channel change request. The channel change stream codedpictures are of a lower quality than the normal stream coded pictures.

According to another aspect of the present invention, in a set top boxcoupled to a Digital Subscriber Line (DSL) system and having a userinterface for transmitting a channel change request, there is provided avideo decoder for enabling a channel change. The video decoder includesa decoder for receiving and decoding a normal stream and a channelchange stream. The normal stream has normal stream coded pictures andthe channel change stream has channel stream coded pictures of a lowerquality than the normal stream coded pictures.

According to yet another aspect of the present invention, in a contentprovider coupled to a Digital Subscriber Line (DSL) system, there isprovided a video encoder for enabling a channel change. The videoencoder includes an encoder for coding a normal stream having normalstream coded pictures and for coding a channel change stream havingchannel change stream coded pictures, such that the channel changestream coded pictures are coded at a lower quality than the normalstream coded pictures.

According to a further aspect of the present invention, in a channelchange processing unit of a Digital Subscriber Line (DSL) system, thereis provided a method for enabling a channel change. The method includesthe steps of: receiving a normal stream and a channel change stream;receiving a channel change request; and sending the channel changestream in response to receiving the channel change request. The channelchange stream coded pictures are of a lower quality than the normalstream coded pictures.

According to a yet further aspect of the present invention, in a set topbox coupled to a Digital Subscriber Line (DSL) system and having a userinterface for transmitting a channel change request, there is provided adecoding method for enabling a channel change. The method includes thesteps of receiving and decoding one of a normal stream and a channelchange stream. The normal stream has normal stream coded pictures andthe channel change stream has channel stream coded pictures of a lowerquality than the normal stream coded pictures.

According to an additional aspect of the present invention, in a contentprovider coupled to a Digital Subscriber Line (DSL) system, there isprovided an encoding method for enabling a channel change. The encodingmethod includes the steps of coding a normal stream having normal streamcoded pictures and coding a channel change stream having channel changestream coded pictures, such that the channel change stream codedpictures are coded at a lower quality than the normal stream codedpictures.

These and other aspects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof exemplary embodiments, which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood in accordance with thefollowing exemplary figures, in which:

FIG. 1 shows a block diagram for an end-to-end architecture inaccordance with the principles of the present invention;

FIG. 2 shows a block diagram for a video encoder with lower resolutionchannel change stream pictures in accordance with the principles of thepresent invention;

FIG. 3 shows a block diagram for a video decoder with lower resolutionchannel change stream pictures in accordance with the principles of thepresent invention;

FIG. 4 shows a block diagram for an alternate video decoder with lowerresolution channel change stream pictures in accordance with theprinciples of the present invention;

FIG. 5 shows a flow diagram for a method for enabling a channel changein a Digital Subscriber Line (DSL) system with prediction drift inaccordance with the principles of the present invention;

FIG. 6 shows a flow diagram for a method for enabling a channel changein a Digital Subscriber Line (DSL) system without prediction drift inaccordance with the principles of the present invention; and

FIG. 7 shows a flow diagram for a method for decoding a channel changestream in a set top box of a Digital Subscriber Line (DSL) System inaccordance with the principles of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is directed to a method and apparatus for enablinga fast channel change for a Digital Subscriber Line (DSL) system. Thatis, the present invention provides a method and apparatus that enable alow delay channel change time in a video over DSL system, whilesignificantly reducing the bitrate over prior methods of enabling lowdelay channel change.

Prior art systems broadcast I pictures frequently to enable channelchange, for example every N pictures. According to the presentinvention, I pictures are used less frequently, and a lower bitratechannel change bitstream is also encoded and stored at the DSL AccessMultiplexer (DSLAM). When a user requests a channel change, the storedlower bitrate channel change bitstream is sent to the user, allowing forrapid channel change, while minimizing the total bitrate over the DSLlocal loop.

The present description illustrates the principles of the presentinvention. It will thus be appreciated that those skilled in the artwill be able to devise various arrangements that, although notexplicitly described or shown herein, embody the principles of theinvention and are included within its spirit and scope.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the principlesof the invention and the concepts contributed by the inventor tofurthering the art, and are to be construed as being without limitationto such specifically recited examples and conditions.

Moreover, all statements herein reciting principles, aspects, andembodiments of the invention, as well as specific examples thereof, areintended to encompass both structural and functional equivalentsthereof. Additionally, it is intended that such equivalents include bothcurrently known equivalents as well as equivalents developed in thefuture, i.e., any elements developed that perform the same function,regardless of structure.

Thus, for example, it will be appreciated by those skilled in the artthat the block diagrams presented herein represent conceptual views ofillustrative circuitry embodying the principles of the invention.Similarly, it will be appreciated that any flow charts, flow diagrams,state transition diagrams, pseudocode, and the like represent variousprocesses which may be substantially represented in computer readablemedia and so executed by a computer or processor, whether or not suchcomputer or processor is explicitly shown.

The functions of the various elements shown in the figures may beprovided through the use of dedicated hardware as well as hardwarecapable of executing software in association with appropriate software.When provided by a processor, the functions may be provided by a singlededicated processor, by a single shared processor, or by a plurality ofindividual processors, some of which may be shared. Moreover, explicituse of the term “processor” or “controller” should not be construed torefer exclusively to hardware capable of executing software, and mayimplicitly include, without limitation, digital signal processor (“DSP”)hardware, read-only memory (“ROM”) for storing software, random accessmemory (“RAM”), and non-volatile storage.

Other hardware, conventional and/or custom, may also be included.Similarly, any switches shown in the figures are conceptual only. Theirfunction may be carried out through the operation of program logic,through dedicated logic, through the interaction of program control anddedicated logic, or even manually, the particular technique beingselectable by the implementer as more specifically understood from thecontext.

In the claims hereof, any element expressed as a means for performing aspecified function is intended to encompass any way of performing thatfunction including, for example, a) a combination of circuit elementsthat performs that function or b) software in any form, including,therefore, firmware, microcode or the like, combined with appropriatecircuitry for executing that software to perform the function. Theinvention as defined by such claims resides in the fact that thefunctionalities provided by the various recited means are combined andbrought together in the manner which the claims call for. Applicant thusregards any means that can provide those functionalities as equivalentto those shown herein.

In accordance with the principles of the present invention, a desiredchannel change delay can be achieved without requiring I pictures to besent as frequently as is performed in prior art systems. Instead, achannel change stream is encoded that includes lower quality codedpictures, in addition to the normal quality coded pictures in the normalstream. In response to a request for channel change, channelchange-stream pictures are sent from a DSLAM to the set-top-box for atransient period, and then normal stream pictures are sent. Each picturein the channel change stream is associated with a normal stream picture,but not all pictures present in the normal stream need to have anassociated picture in the channel change stream. Coded pictures in thechannel change stream may be optionally, but not necessarily, coded at alower resolution than pictures in the normal stream. I pictures occurmore frequently in the channel change stream, to enable more frequentrandom access. The most recent I picture and the P and B picturessubsequently coded, if any, may be optionally, but not necessarily,stored at the DSLAM. An I picture and the P and B pictures codedsubsequently to the I picture are referred to as a Group of Pictures(GOP).

Turning to FIG. 1, an exemplary end-to-end architecture to which thepresent invention may be applied is indicated generally by the referencenumeral 100. The architecture 100 includes a content provider 110, aregional broadband network 120, a digital subscriber line accessmultiplexer (DSLAM) 130, a local loop 140, and a set top box (STB) 150.The content provider 110 includes a video encoder 112 having a first anda second output in signal communication with a first and second input,respectively, of a multiplexer 114. An output of the multiplexer 114provides an output of the content provider 110, which is connected insignal communication with the regional broadband network 120. Theregional broadband network 120 is further connected in signalcommunication with an input of the DSLAM 130.

The DSLAM 130 includes a demultiplexer 132 having a first output insignal communication with a first input of a selector 134 and a secondoutput in signal communication with an input of a local storage device136. An output of the storage device 136 is connected in signalcommunication with a second input of the selector 134. A first input ofthe DSLAM 130 is connected in signal communication with an input of thedemultiplexer 132, a second input of the DSLAM 130 is connected insignal communication with a third input of the selector 134, and anoutput of the DSLAM 130 is connected in signal communication with anoutput of the selector 134. The second input and the output of the DSLAM130 are connected in signal communication with the local loop 140. It isto be appreciated that the DSLAM 130 is also interchangeably referred toherein as a “channel change processing unit”.

The STB 150 includes a user interface 152 and a video decoder 154. Anoutput of the STB 150 is connected in signal communication with thelocal loop 140 and with the user interface 152, and an input of the STB150 is connected in signal communication with the local loop 140 andwith the video decoder 154.

The video encoder 112 creates both a normal stream and a channel changestream of coded pictures. The normal stream and channel change streamare multiplexed 114 together and transmitted over a regional broadbandnetwork 120 to the DSLAM 130. For the sake of simplicity with respect toFIG. 1, only a single program's encoder is shown. In an actual system,multiple programs are supported and, thus, blocks in the figure areduplicated for each supported program. A user makes a channel changerequest through the user interface 152 in the STB 150, to indicate aswitch to a new program to be viewed. This request is forwarded to theDSLAM 130.

In a preferred embodiment of the present invention, the channel changestream is stored in storage local (e.g., local storage device 136) tothe DSLAM 130 (or remote storage which may be quickly accessed by theDSLAM 130). During normal viewing, the normal stream is transmitted overthe local loop 140 to the video decoder 154 at the STB 150. When achannel change request is initiated by the user interface of the STB150, it is sent to the DSLAM 130 through the local loop 140. Uponreceiving the channel change request, the DSLAM 130 begins to send thestored channel change stream of the new program to the STB 150,beginning with an I picture in the channel change stream, instead of thenormal stream. Then, at a later point, the DSLAM 130 switches back totransmitting the normal stream to the STB 150.

In one embodiment of the current invention, the switch back totransmitting the normal stream is done once an I picture is available inthe normal stream. In this case, an entire Group Of Picture's (GOP's)worth of channel change stream coded pictures are used after a channelchange request. When used in an embodiment that includes storage of thechannel change pictures at the DSLAM, a new I picture in the channelchange stream is received at the DSLAM 130, the previously storedchannel change stream coded pictures may be replaced with the picturesin the new GOP.

In another embodiment, only I pictures are present in the channel changestream, and the switch back to the normal stream takes place immediatelyafter the channel change stream I picture is sent. In this case, only asingle channel change stream I coded picture needs to be stored. When anew I picture in the channel change stream is received, it may replacein the storage the previously stored channel change stream I picture.

Sending the channel change stream in addition to the normal streamincreases the bandwidth requirement over the regional broadband network120. However, reducing the frequency with which I pictures are coded inthe normal stream reduces the bandwidth requirement for the normalstream. Over the more highly constrained local loop 140, pictures in thechannel change stream are only transmitted when normal pictures are not,so a reduction in bandwidth in the local loop 140 is always observed inaccordance with this invention versus the prior art. In addition,channel change latency is reduced. In a prior art system, playback aftera channel change could only begin after an I picture for the new programwas received at the STB 150. There are several components associatedwith that delay, including the period of time until the DSLAM 130receives a new I picture in the bitstream and begins to send it to theSTB 150, and until the entire I picture is received at the STB 150.Because I pictures are typically larger than other coded picture types,the transmission delay is typically larger than the coded picture rate.The present invention may reduce both of these two identified componentsof the channel change latency. First, because the channel change streamI pictures are of a lower bitrate than normal I pictures, they may occurmore frequently in the bitstream, reducing the waiting time until a newI picture is available. Secondly, because the channel change streamcoded pictures are of a lower bitrate than the normal stream codedpictures, the transmission time for the first channel change I pictureto be received at the STB 150 is reduced.

Since the channel change stream coded representation of the videosequence is of a lower quality than the normal stream, the user willexperience lower video quality during a short transition periodimmediately following a channel change request. After this initialtransition period, the full quality of the normal stream is observed. Ifonly I pictures are present in the channel change stream, the subsequentP and B pictures in the normal stream are decoded using the channelchange I picture, which differs from the normal stream I picture thatthey were encoded with respect to, resulting in prediction drift.

The coded pictures in the channel change stream may be of lowerresolution than the pictures in the normal stream, in which case theyare upsampled at the video decoder 154 prior to storing in the referencepicture stores. The video decoder 154 must be signaled in some way thatupsampling should be performed, for example an additional parametercould be added to the slice header.

Turning to FIG. 2, a video encoder 200 with lower resolution channelchange stream pictures is indicated generally by the reference numeral200. In the video encoder 200, channel change stream pictures are codedat a lower quality and possibly lower resolution than normal streampictures. Lower quality could be achieved through the use of higherquantizer values, or the use of the Reduced Resolution Update mode. Aninput of the video encoder 200 is connected in signal communication witha first input of a normal video encoder 210. A second input of thenormal video encoder 210 is connected in signal communication with anoutput of frames stores 215. An output of the normal video encoder 210is connected in signal communication with an input of the frames stores215. The output of the normal video encoder 210 is also an externallyavailable output of the video encoder 200. The input of the videoencoder 200 is further connected in signal communication with an inputof an optional downsampler 220. An output of the downsampler 220 isconnected in signal communication with a first input of a low qualityencoder 230. It is to be appreciated that in the event that optionaldownsampler 220 is not employed, then the input of the encoder 200 isfurther connected in signal communication with the first input of thelow quality encoder 230. A second input of the low quality encoder 230is connected in signal communication with an output of frames stores260. An output of the low quality encoder 230 is connected in signalcommunication with an input of the frames stores 260. The output of thelow quality encoder 230 is also an externally available output of thevideo encoder 200.

The optional downsampler 220 reduces the resolution of the input video,and the downsampled video is encoded using the lower quality encoder230, to create the channel change stream. The selection of encoding achannel change picture at lower resolution can be done at the encoderand can depend on the bitrate and quality requirements set by thebroadcast provider. The input video is encoded with the normal videoencoder 210 to create the normal stream.

Turning to FIG. 3, a video decoder with lower resolution channel changestream pictures is indicated generally by the reference numeral 300. Inthe video decoder 300, channel change stream pictures are coded at alower resolution than the normal stream pictures. An input of the videodecoder 300 is connected in signal communication with a first input of avideo decoder 310. A second input of the video decoder 310 is connectedin signal communication with an output of frames stores 320. An outputof the video decoder 310 is connected in signal communication with aninput of frames stores 320. The output of the video decoder 310 isfurther connected in signal communication with an input of an upsampler330, and with a first input of a selector 340. An output of theupsampler 330 is connected in signal communication with a second inputof the selector 340. An output of the selector 340 is an externallyavailable output of the decoder 300. Either the normal stream or thechannel change stream coded pictures are decoded, and the decodedpictures are stored in the frame stores 320. If the current picture isfrom the channel change stream, it might be required that the currentpicture is upsampled prior to display. If the current picture is fromthe normal stream, upsampling is unnecessary, and the decoded picture isdisplayed. This system applies when after a channel change, the DSLAM130 switches back to the normal stream when an I picture is being sent.

Turning to FIG. 4, an alternate video decoder with lower resolutionchannel change stream pictures is indicated generally by the referencenumeral 400. An input of the video decoder 400 is connected in signalcommunication with a first input of a video decoder 410. A second inputof the video decoder 410 is connected in signal communication with anoutput of frames stores 420. An output of the video decoder 410 isconnected in signal communication with an input of an upsampler 430 andwith a first input of a selector 440. An output of the upsampler 430 isconnected in signal communication with a second input of the selector440. An output of the selector 440 is connected in signal communicationwith an input of the frames stores 420. The output of the selector 440is an externally available output of the decoder 400.

The alternative video decoder 400 is used when the first normal streampictures transmitted after the channel change are P or B pictures, inwhich case prediction drift occurs. This is because the P and B picturesare decoded at the video decoder using the channel change I picture as areference rather than the normal stream I picture with which those P andB pictures were encoded with respect to. In this case, the lowresolution channel change stream picture is upsampled after decoding.The upsampled pictures are used for display and are also stored in theframe stores for use in decoding later normal stream pictures. Againwhen normal stream coded pictures are decoded, no upsampling isnecessary.

The channel change stream coded video sequence may be at a lower framerate than the normal stream, that is, fewer coded pictures may bepresent in the channel change stream than in the normal stream. Thevideo decoder may simply display those pictures that it receives fromthe channel change stream for additional picture display times.

If a Reduced Resolution Update video encoder and decoder are employed,the upsampling and downsampling blocks that already exist in the encoderand decoder may be reused for the channel change stream pictureupsampling.

When the channel change stream GOP is stored in the DSLAM 130, itsassociated audio is also stored. When the channel change stream videocoded pictures are selected for transmission to the STB 150, the audioassociated with those pictures is also transmitted.

Turning to FIG. 5, in a Digital Subscriber Line Access Multiplexer(DSLAM) of a DSL system with prediction drift, a method for enabling achannel change is indicated generally by the reference numeral 500. Abegin block 510 passes control to a decision block 520, which determineswhether or not a channel change request has been received to play acurrent program. If the channel change request has not been received,then control passes back to decision block 520. Otherwise, if thechannel change request has been received, then control passes to afunction block 530 that sends a channel change stream coded I picture.The function block 530 passes control to a function block 540 that sendsa normal stream coded picture. The function block 540 passes control toa decision block 550 that determines whether or not a channel changerequest has been received to exit a current program. If the channelchange request has not been received, then control passes back tofunction block 540. Otherwise, if the channel change request has beenreceived, then control passes to an end block 560.

Turning to FIG. 6, in a Digital Subscriber Line Access Multiplexer(DSLAM) of a DSL system without prediction drift, a method for enablinga channel change is indicated generally by the reference numeral 600. Abegin block 610 passes control to a decision block 620 that determineswhether or not a channel change request has been received to play acurrent program. If the channel change request has not been received,then control passes back to the decision block 620. Otherwise, if thechannel change request has been received, then control passes to afunction block 630 that sends a channel change stream coded picture. Thefunction block 630 passes control to a decision block 640 thatdetermines whether or not an I picture is available in the normalstream. If an I picture is not available, then control passes back tofunction block 630. Otherwise, if an I picture is available, thencontrol passes to a function block 650 that sends a normal stream codedpicture. The function block 650 passes control to a decision block 660that determines whether or not a channel change request has beenreceived to exit a current program. If the channel change request hasnot been received, then control passes back to the decision block 640.Otherwise, if the channel change request has been received, then controlpasses to an end block 670.

Turning to FIG. 7, a method for decoding a channel change stream in aset top box of a Digital Subscriber Line (DSL) System is indicatedgenerally by the reference numeral 700. The DSL system includes a DSLAccess Multiplexer (DSLAM). A begin block 710 passes control to adecision block 720 that determines whether or not a user request hasbeen received to change a channel or turn on a set top box. If the userrequest has not been received, then control passes back to decisionblock 720. Otherwise, if the user request has been received, thencontrol passes to a function block 730 that sends the request to theDSLAM for the desired program. The function block 730 passes control toa function block 740 that receives and decodes a picture, and passescontrol to a decision block 750. The decision block 750 determineswhether or not the decoded picture is a channel change stream picture oflower resolution than the normal stream. If the decoded picture is achannel change stream picture of lower resolution than the normalstream, then control passes to a function block 760 that upsamples thechannel change stream picture. Otherwise, if the decoded picture is nota channel change stream picture of lower resolution than the normalstream, then control passes to a decision block 770 that determineswhether or not a user request has been received to change to a differentchannel or to turn off the set top box. If the user request has not beenreceived, then control passes back to function block 740. Otherwise, ifthe user request has been received, then control passes to an end block780.

It is to be appreciated that the present invention may be applied totransmission systems other than DSL systems, while maintaining thespirit of the present invention. The key requirements for applicationare that the video encoder be connected via a network to a channelchange processing unit. The channel change processing unit is in turnconnected via a network to a video decoder.

A description will now be given of some of the many attendantadvantages/features of various embodiments of the present invention. Forexample, an advantage/feature an embodiment of the present invention isa channel change processing unit that receives normal stream and channelchange stream, stores the channel change stream, and sends the channelchange stream pictures following a channel change request. Anotheradvantage/feature of an embodiment of the present invention is a channelchange processing unit as described above, wherein the first codedpicture sent from the channel change stream is an I picture. Yet anotheradvantage/feature associated with an embodiment of the present inventionis a channel change processing unit as described above, wherein thechannel change stream coded pictures are of lower resolution than thenormal stream coded pictures. A further advantage/feature associatedwith an embodiment of the present invention is a channel changeprocessing unit as described above, wherein the channel change streamcoded pictures are of lower frame rate than the normal stream codedpictures. Another advantage/feature associated with an embodiment of thepresent invention is a channel change processing unit as describedabove, wherein the channel change stream coded pictures are coded at alower bitrate than the normal stream pictures. Still anotheradvantage/feature associated with an embodiment of the present inventionis a channel change processing unit as described above, wherein thechannel change stream coded pictures use RRU. Moreover, anotheradvantage/feature associated with an embodiment of the present inventionis a channel change processing unit as described above, wherein only anI picture is stored and sent in the channel change stream following achannel change request. Furthermore, another advantage associated withan embodiment of the present invention is a channel change processingunit as described above, wherein after the channel change streampictures are sent, a switch is made to sending the normal streampictures. Still another advantage associated with an embodiment of thepresent invention is a channel change processing unit as describedabove, wherein a single GOP's worth of channel change pictures arestored, and then are replaced as a new GOP arrives.

These and other features and advantages of the present invention may bereadily ascertained by one of ordinary skill in the pertinent art basedon the teachings herein. It is to be understood that the teachings ofthe present invention may be implemented in various forms of hardware,software, firmware, special purpose processors, or combinations thereof.

Most preferably, the teachings of the present invention are implementedas a combination of hardware and software. Moreover, the software ispreferably implemented as an application program tangibly embodied on aprogram storage unit. The application program may be uploaded to, andexecuted by, a machine comprising any suitable architecture. Preferably,the machine is implemented on a computer platform having hardware suchas one or more central processing units (“CPU”), a random access memory(“RAM”), and input/output (“I/O”) interfaces. The computer platform mayalso include an operating system and microinstruction code. The variousprocesses and functions described herein may be either part of themicroinstruction code or part of the application program, or anycombination thereof, which may be executed by a CPU. In addition,various other peripheral units may be connected to the computer platformsuch as an additional data storage unit and a printing unit.

It is to be further understood that, because some of the constituentsystem components and methods depicted in the accompanying drawings arepreferably implemented in software, the actual connections between thesystem components or the process function blocks may differ dependingupon the manner in which the present invention is programmed. Given theteachings herein, one of ordinary skill in the pertinent art will beable to contemplate these and similar implementations or configurationsof the present invention.

Although the illustrative embodiments have been described herein withreference to the accompanying drawings, it is to be understood that thepresent invention is not limited to those precise embodiments, and thatvarious changes and modifications may be effected therein by one ofordinary skill in the pertinent art without departing from the scope orspirit of the present invention. All such changes and modifications areintended to be included within the scope of the present invention as setforth in the appended claims.

What is claimed is:
 1. A method for enabling a channel changecomprising: accessing a normal stream and a channel change stream,wherein the normal stream and the channel change stream correspond to asingle video program and are multiplexed together before transmission toa decoder; receiving a channel change request from a viewing location atwhich the normal stream and the channel change stream are viewed by aviewer; and selecting and second the channel change stream to theviewing location in response to receiving the channel change request,wherein the channel change stream coded pictures are of a lower qualitythan the normal stream coded pictures, wherein a first coded picture inthe channel change stream sent to the viewing location in response toreceiving the channel change request is an I picture, and wherein saidselecting limits an amount of data by selecting, at any given time, onlyone of the normal stream and the channel change stream to send to theviewing location for viewing by the viewer.
 2. The method as defined inclaim 1, further comprising the step of locally storing the channelchange stream.
 3. The method as defined in claim 1, wherein the channelchange stream includes channel change stream coded pictures, the normalstream includes normal stream coded pictures, and the channel changestream coded pictures are of a lower resolution than the normal streamcoded pictures.
 4. The method as defined in claim 1, wherein the channelchange stream includes channel change stream coded pictures, the normalstream includes normal stream coded pictures, and the channel changestream coded pictures are of a lower frame rate than the normal streamcoded pictures.
 5. The method as defined in claim 1, wherein the channelchange stream includes channel change stream coded pictures, the normalstream includes normal stream coded pictures, and the channel changestream coded pictures are coded at a lower bitrate than the normalstream coded pictures.
 6. The method as defined in claim 1, wherein thechannel change stream includes channel change stream coded pictures thatuse Reduced Resolution Update.
 7. The method as defined in claim 1,wherein said sending step comprises the step of sending only an Ipicture in the channel change stream in response to receiving thechannel change request.
 8. The method as defined in claim 1, wherein thechannel change stream includes channel change stream coded pictures, thenormal stream includes normal stream coded pictures, and said sendingstep comprises the step of sending the normal stream coded picturesafter the channel change stream coded pictures have been sent.
 9. Themethod as defined in claim 2, wherein said storing step comprises thestep of storing channel change stream coded pictures for a single Groupof Pictures (GOP), and the method further comprises the step ofreplacing the channel change stream coded pictures for the GOP as a newGOP is received.